908 DR. R. W. SHUFELDT ON THE OSTEOLOGY OF THE [DeC. 1, 



presenting all the characters of this part common to the avian 

 hrachium. As will be seen from the figure, the ulna and radius 

 present nothing peculiar. The free bones in the carpus are two in 

 number, as is the rule for birds. The metacarpus offers us nothing 

 worthy of special note, as may be seen from the drawing. The poUex- 

 phalanx is composed of but one joint, the index-digit of two ; and 

 tlie usual small one in tlie next finger. Tl>e expanded portion of 

 the proximal phalanx of the index shows two perforations ; these run 

 into one large one in Nuttail's Whippoorwill — a rare condition. 



This last-named bird has the skeleton of its arm, with the excep- 

 tion of this one detail, agreeing in all essential respects with the 

 bones just described. Pueumaticity does not extend beyond the 

 humerus in true Caprimulgidcs. 



Turning our attention to the Humming-birds, we find that the 

 humerus in Trochilns is a most extraordinary structure, departing, as 

 it does, both in form and proportions, from that bone as it occurs 

 in most birds. The humeral head for the glenoid cavity has much 

 the same contour as elsewhere in the class ; but the radial crest is 

 represented by a strong and gracefully curved hook curling over in 

 the direction of the shaft. Another prominent process points for- 

 wards and outwards, which has its base just beyond the distal por- 

 tion of the periphery of the pneumatic foramen. Eccentricities of 

 form are none the less evident in the shaft of this unique bone. 

 This is of a quadrilateral outline, broadly oblong, and somewhat 

 curiously twisted. 



The trochleae of the distal end are very prominent, while opposite 

 them on the anconal aspect, is found, holding a mid position, a deep 

 and rounded excavation. In life this harbours a large sesamoid ; 

 and another, about one third its size, is at the elbow (Plate LXI. 

 figs. 3 s, s'). 



The radius and ulna are but little longer than the humerus ; the 

 former is much bowed, giving rise to a large "interosseous space" 

 when these bones are duly articulated. The ulna is nearly straight, 

 having a stout, subcylindrical shaft; and notwithstanding the presence 

 of the sesamoid in the olecranon fossa of the humerus, the process 

 of this name is well developed upon it. 



Two small sesamoids are found about the carpal joint («", s"), 

 while its true elements, the ulnare and radiate, are manifestly dif- 

 ferent from these segments in ordinary birds, the former in being 

 almost devoid of the characteristic apophyses, and the latter in being 

 less angular. 



This Humming-bird has a metacarpus notably longer than the 

 bones of its antibrachium. Its iiidex and midshaft are quite straight 

 {i , tn), the latter being produced further distally, and supporting a 

 considerable facet for its unusually long finger-joint >h" (compare with 

 figure 4). The pollex-digit has but one joint (p), two being awarded 

 to the index, the proximal one of the latter having its blade portion 

 very much expanded and a mid process (_;') at its lower margin — an 

 uncommon site for it. 



Comparing these points in the skeleton of the arm of T. alexandri. 



